This proposal is about the perception and learning by infants of relationships between events in different sensory modalities. At least some of the correspondences that infants perceive between auditory and visual stimuli are not arbitrary. Six-month old infants perceive a synesthetic relationship between the-dimensions of auditory pitch and visual location: high pitch is perceived as corresponding with high visual location, and low pitch with low visual location. The major focus of this proposal is on biological constraints that may operate on the perception and learning of auditory-visual relationships. Although the primary goal is to further knowledge about the development of synesthetic perception in normal infants, the results could be potentially used in the future to design methods of facilitating perception in the sensory-impaired. The project has two specific aims: 1) Infants at 3, 6, and 12 months of age will be studied in order to get a picture of the developmental course of synesthetic abilities. The studies would provide data that address the problem of the origin of intermodal abilities. 2) The ability of infants to learn specific auditory-visual relationships will be investigated. Infants may be biologically prepared to learn synesthetically congruent relationships more readily than synesthetically incongruent relationships. Two methods will be used to address these issues. In the first method, infants' visual reaction times to look at pictures will be measured while the infants are simultaneously presented with an auditory stimulus. It is expected that reaction times to look at pictures with a synesthetically congruent relationship between sound and picture will be faster than reaction times to pictures with a synesthetically incongruent sound-picture relationship. The second method will measure the looking preference of infants for two pictures which are presented simultaneously while the infant is also presented with a sound. It is expected that the infants will prefer to look at the picture that synesthetically corresponds to the sound.